Hydrocracking processes for the conversion of heavy hydrocarbon oils to light and intermediate naphthas of good quality for reforming feedstocks, fuel oil and gas oil are well known. These heavy hydrocarbon oils can be such material as petroleum crude oils, atmospheric tar bottoms products, vacuum tar bottoms products, heavy cycle oils, shale oils, coal-derived liquids, crude oil residua, topped crude oils and heavy bituminous oils extracted from oil sands. Of particular interest are oils which contain a large portion of material boiling above 524.degree. C. equivalent atmospheric boiling point.
As the reserves of conventional crude oils decline, these heavy oils must be upgraded to meet the demands. In this upgrading, the heavier material is converted to lighter fractions and most of the sulphur, nitrogen and metals must be removed.
This has been done either by a coking process, such as delayed or fluidized coking, or by a hydrogen addition process such as thermal or catalytic hydrocracking. The distillate yield from the coking process is about 70 wt % and this process yields a significant amount of low-BTU gas and coke as byproduct.
Work has also been done on an alternative processing route involving hydrogen addition at high pressures and temperatures and this has been found to be quite promising. In thermal hydrocracking, the major problem is coke or solid deposition in the reactor, especially when operating at relatively low pressure and this can result in costly shut-downs. Higher pressure reduces reactor fouling but plant operations at high pressure involve higher capital and operating costs.
It has been well established that mineral matter present in the feedstock plays an important role in coke deposition. Chervenak et al., U.S. Pat. No. 3,775,296 shows that feed containing high mineral content (3.8 wt %) has less tendency to form coke in the reactor than feed containing low mineral matter (&lt;1 wt %). The addition of coke carriers was proposed in Schuman et al. U.S. Pat. No. 3,151,057, who suggested the use of "getters" such as sand, quartz, alumina, magnesia, zircon, beryl or bauxite. It has been shown in Ternan et al., Canadian Patent No. 1,073,389 and Ranganathan et al., U.S. Pat. No. 4,214,977 that the addition of coal and coal-based catalyst results in the reduction of coke deposition during hydrocracking.
In U.S. Pat. No. 3,775,286 a process is described for hydrogenating coal in which the coal was either impregnated with hydrated iron oxide, or dry, hydrated iron oxide powder was physically mixed with powdered coal. Canadian Patent No. 1,202,588 describes a process for hydrocracking heavy oils in the presence of an additive in the form of dry mixture of coal and an iron salt, such as iron sulphate.
Dry grinding of coal and/or drying of coal impregnated with iron salt and/or drying of coal and iron compound mixture is a hazardous and difficult procedure. To over
come this problem, a procedure was described in Khulbe et al, U.S. patent application Ser. No. 304,557, filed Feb. 1, 1989 to form an additive by grinding a coal and an iron compound mixture under oil. Although this procedure avoids the problems associated with wet impregnation and subsequent drying of coal particles, still the problems associated with the handling of coal and coal dust exist.